Models
Xbox 360 S: 250GB/$299.99
Xbox 360 Elite: 120GB/$249.99 (No word on how long the Elite will stick around.)
Xbox 360 Arcade: 256MB/$149.99 (Does not reflect new design but MS says a revamped Arcade model is on the way. No word on what features will be transferred over from the S.)

PS3 250GB: $349.99
PS3 120GB: $299.99

Only the new Xbox 360 S has a removable hard drive. However, Xbox 360 external hard drives and memory units are not compatible. See how to transfer data to the new Xbox 360 S here.